Patent GB-1135291-A (GB)
Title: Electronic simulator for fluid pressure and flow in the cylinders of reciprocating compressors
IPC: G06G7/64
Filed: 1966-02-03
Abstract: 1,135,291. Electric analogue simulator for compressors. SNAM PROGETTI S.p.A. 3 Feb., 1966 [14 May, 1965], No. 4864/66. Heading G4G. [Also in Divisions H2 and H3] In simulation of fluid pressure and flow in a compressor cylinder (Fig. 1, not shown) a sinusoidal generator of voltage E energizes a variable capacitor C simultating the cylinder volume in series with a variable resistor R; the capacitor being shunted by a first diode representing the intake valve in series with positive direct voltage Va representing intake pressure, and also shunted by a second reversed poled diode representing the delivery valve in series with positive direct voltage V M  representing delivery pressure. Initially at time t = o the capacitor charges to V A  (Fig. 1a, not shown) and charges further from the generator according to law while V A  <Vi <V M  and the diodes are reconducting, until V c  = V M  and the second diode passes current i M  simulating delivery flow until t =T/2; V c  remaining = V M .   On subsequent polarity reversal, the second diode cuts off and since V C  > V A  the first diode is also cut off. The voltage V c  is reduced according to the law until Vi = V A  T/2 and the first diode conducts to pass current i A  simulating intake flow, until i is again returned to zero and V c  remains constant = V A . The cycle recommences with the delivery and intake current pulses having equal duration. More accurately, a compressor is simulated by the circuit of Fig. 2 wherein two simulator circuits are provided separately representing intake and delivery phases and comprises (1) capacitor 2<SP>1</SP> fed through resistance 7<SP>1</SP> from point 10 of a centre tapped transformer, diode 4<SP>1</SP> connected directly to unidirectional voltage V A , diode 3<SP>1</SP> in series therewith and connected to unidirectional voltage V M  over transistorized impedance transducer circuit 9 (Fig. 3b, not shown); capacitor 2<SP>1</SP> being switchable between the junction of the diodes and the outlet 16. (2) Capacitor 2<SP>11</SP> fed through resistance 7<SP>11</SP> from point 10, diode 4<SP>11</SP> connected to unidirectional voltage V A  over transistorized impedance transducer circuit 8 (Fig. 3b, not shown), diode 3<SP>1</SP> in series therewith and connected directly to unidirectional voltage V M . The transducer circuits pass voltage between their inputs and outputs but exclude currents therethrough so that the two simulator circuits are inter-connected only by voltages V M , V A  representing delivery and intake pressures. In synchronism with the alternating voltage at point 10 (Fig. 4a) (a) voltages V 13 , V 14 , (d, e) appear across the capacitors increasing from V A  to V M  with differing slopes corresponding to the values of parameters 7<SP>11</SP>, 2<SP>11</SP>, 7<SP>1</SP>, 21 representing the distinct delivery and intake characteristics of the compressor. Initially, capacitors 2<SP>1</SP>, 2<SP>11</SP> are charged to voltage V A , and 2<SP>1</SP> is charged up to V M  before 2<SP>11</SP> by the alternating voltage at point 10. When V 14  = V M  diode 3<SP>1</SP> opens but no current flows from source 6 by reason of impedance transducer 9. When V 13  = V M , however, current i M  commences to flow from 6 for the remainder of the first half-cycle (Fig. 4a) (g); the capacitors being held to V M . When during the second half-cycle, V 14  = V A , current i A  flows from 5, but when V 13  = V A  no current flows therefrom by reason of impedance transducer 8 (Fig. 4a) (h). Thus intake flow is simulated by current i A  in simulation circuit 7<SP>1</SP>, 2<SP>1</SP>, 3<SP>1</SP>, 4<SP>1</SP> and delivery flow is simulated by current i M  in simulation circuit 7<SP>11</SP>, 2<SP>11</SP>, 3<SP>11</SP>, 4<SP>11</SP>. The durations of flow of i A , i M  are variable with parameters 7<SP>11</SP>, 2<SP>11</SP> and 71, 2<SP>1</SP> respectively. The voltages appearing across capacitors 2<SP>1</SP>, 2<SP>11</SP> are applied together with antiphased alternating voltages from points 10, 11 (Fig. 41a) (a, b) to a gating modulator 28 (Fig. 4b, not shown) operating to select at output 15 the voltage arising at 3 during the first half-cycle and the voltage at during the second half-cycle of excitation, to produce a voltage V 15  (Fig. 4a) (f) which is displayed on an oscillograph against an X timebase voltage derived at point 12 from the energization voltage but phase shifted 90 degrees over resistance 17 and capacitance 18 to represent the winch cycle of the compressor (Fig. 5) of pressure against volume where A is the intake phase, M the delivery phase, P M  the delivery pressure and P A  the intake pressure; the adiabatic curves of compression being approximated by straight lines. Where in a single acting compressor cylinder the intake is ducted to the inactive volume below the piston, or in a double acting compressor it is ducted to the second section of the cylinder over a permanently open intake valve, the duct circulation flow may be simulated by operating switch 19 to develop at 16 a sinusoidal current phase shifted 90 degrees from the current simulating intake flow in the compressor cylinder, and adjustable in amplitude by variation of parameters 7<SP>1</SP>, 2<SP>1</SP>. Measurement of mean values of delivery and intake currents I M , I A  and observation of the work cycle enables the parameters of the simulating circuits to be varied for optimum performance so that corresponding parameters of an actual compressor may be determined. LCR lines may be introduced into intake and delivery to simulate ducting. Where a compressor comprises plural cylinders mechanically coupled with angular phase shift therebetween, each cylinder is represented by the circuit of Fig. 2, energized with alternating voltage having corresponding phase shifts. These are derived from a circuit (Fig. 6) wherein an oscillator 20 incorporating a rectangular hysteresis loop magnetic core generates frequency f<SP>1</SP> proportional to an input voltage V i . A flip-flop multivibrator divider 21 and diode decoding matrix 22 develop rectangular pulses at frequency f=f1/n at phase shifts of 360 degrees/n  at n outputs, and a phase selector switch 23 extracts the ith and (i + n/2)th pulses to control a flip-flop multivibrator 24 producing a symmetrical rectangular wave of frequency f of appropriate phase which is clipped to the amplitude of Vi at 25, integrated to a constant amplitude triangular waveform at 26, and converted by a non-linear diode and resistor line 27 to a sine wave of constant amplitude and the selected phase. Plural phase selectors 23 and processing chains 24 to 27 produce the requisite series of energization voltages.